The present invention relates to a wire, generally a steel wire, provided with a surface coating of a metal alloy. The invention also relates to a process put into practice for carrying out surface-treating of the wire in question and a composite element obtained by incorporating wires made in accordance with the present invention into an elastomeric matrix.
It is known that in the manufacture of rubber articles, such as tires for motor-vehicles and the like, composite structural elements are widely used, that is elements made up of a matrix of an elastomeric material into which a plurality of wires or metallic cords each consisting of a plurality of said wires are incorporated, the function of which is to give the structural element the necessary features in terms of structural strength and geometrical stability.
The wires used for this purpose, generally steel wires, are obtained as a result of a drawing operation carried out at several different times until the desired size is reached, and usually have a coating of a metal alloy on their surface, the essential functions of said coating consisting in promoting the drawing capability of the wire and the adhesion of the elastomeric matrix to the coated wire.
To this end, different modalities for making the wire coating have been proposed.
For example, European Patent EP 296,036 deals with a wire coating made of copper, brass, tin, zinc or alloys thereof also containing nickel or cobalt for the purpose of improving adhesion of the elastomeric material to the wire.
In European Patent EP 283,738, filed in the name of the same Applicant, a wire coating is disclosed which consists of two superposed layers made of a nickel/zinc alloy wherein, in the inner layer, the zinc content is between 60% and 90% and in the outer layer the nickel content is in the range of 60% to 80%. In the same patent the possibility of replacing nickel with cobalt in the nickel/zinc alloy is suggested.
In French patents FR 2,413,228 and FR 2,426,562 a wire coated with a ternary alloy consisting of brass and cobalt is described, in which the cobalt content is between 0.5% and 30%.
In U.S. Pat. No. 2,296,838 the wire coating consists of an inner layer and an outer layer, made of zinc and cobalt respectively.
U.S. Pat. No. 4,218,517 illustrates the application to a wire of a coating made of a copper/cobalt alloy in which the copper content is in the range of 10% to 70%.
Finally, U.S. Pat. No. 4,872,932 pertains to a method of making composite elements of an elastomeric material essentially consisting of a support and a matrix of an elastomeric material fastened thereto. In this manufacturing method a film of a thickness included between 10 .ANG. and 100 .mu.m, made of a zinc/cobalt alloy with a cobalt content higher than 80% is provided to be deposited on said support.